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  • Python: Repeat elements in a list comprehension?

    - by User
    I have the following list comprehension which returns a list of coordinate objects for each location. coordinate_list = [Coordinates(location.latitude, location.longitude) for location in locations] This works. Now suppose the location object has a number_of_times member. I want a list comprehension to generate n Coordinate objects where n is the number_of_times for the particular location. So if a location has number_of_times = 5 then the coordinates for that location will be repeated 5 times in the list. (Maybe this is a case for a for-loop but I'm curious if it can be done via list comprehensions)

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  • python conditional list creation from 2D lists

    - by dls
    Say I've got a list of lists. Say the inner list of three elements in size and looks like this: ['apple', 'fruit', 1.23] The outer list looks like this data = [['apple', 'fruit', 1.23], ['pear', 'fruit', 2.34], ['lettuce', 'vegetable', 3.45]] I want to iterate through the outer list and cull data for a temporary list only in the case that element 1 matches some keyword (aka: 'fruit'). So, if I'm matching fruit, I would end up with this: tempList = [('apple', 1.23), ('pear', 2.34)] This is one way to accomplish this: tempList = [] for i in data: if i[1] == 'fruit': tempList.append(i[0], i[2]) is there some 'Pythonic' way to do this in fewer lines?

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  • Fastest way to check a List<T> for a date

    - by fishhead
    I have a list of dates that a machine has worked on, but it doesn't include a date that machine was down. I need to create a list of days worked and not worked. I am not sure of the best way to do this. I have started by incrementing through all the days of a range and checking to see if the date is in the list by iterating through the entire list each time. I am looking for a more efficient means of finding the dates. class machineday { datetime WorkingDay; } class machinedaycollection : List<machineday> { }

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  • Display/Hide part of a list

    - by superexsl
    Hi I have an (unordered)list (generated by a repeater) of items. However, I'd like to show the first three items, and have the rest hidden by the main content div. When a button is pressed, I would like the list's div to expand, pushing the main content div down and showing the rest of the list. I was thinking of using slideDown(), but that closes the entire div ( and I would like to show the first 3 items of the list). What would be the best way to achieve an effect like this? Is there a plugin that can easily show X items of a list and the display the rest upon request? Thanks

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  • Best way to implement a List(Of) with a maximum number of items

    - by Ben
    I'm trying to figure out a good way of implementing a List(Of) that holds a maximum number of records. e.g. I have a List(Of Int32) - it's being populated every 2 seconds with a new Int32 item. I want to store only the most current 2000 items. How can I make the list hold a maximum of 2000 items, then when the 2001'th item is attempted to be added, the List drops the 2000'th item (resulting in the current total being 1999). Thing is, I need to make sure I'm dropping only the oldest item and adding a new item into the List. Ben

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  • Trim email list into domain list

    - by hanjaya
    The function below is part of a script to trim email list from a file into domain list and removes duplicates. /* define a function that can accept a list of email addresses */ function getUniqueDomains($list) { // iterate over list, split addresses and add domain part to another array $domains = array(); foreach ($list as $l) { $arr = explode("@", $l); $domains[] = trim($arr[1]); } // remove duplicates and return return array_unique($domains); } What does $domains[] = trim($arr[1]); mean? Specifically the $arr[1]. What does [1] mean in this context? How come variable $arr becomes an array variable?

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  • Java, searching within a list of objects?

    - by Rick
    I'm a bit lost on the way to make this happen the fastest. I have a large list of objects that have basic variable attributes (with getters / setters) and I need to do a search in this list to find the objects within the list that match a given parameter I have found how to do a regular list search but I need to, for example search for the value of the result of doing a call getName() for each object in the list and get objects that have a result that matches my input. Something like below where the third argument is the result of the method call and the second is what I am trying to find. int index = Collections.binarySearch(myList, "value", getName()); Any advice is appreciated

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  • Using a Loop to add objects to a list(python)

    - by Will
    Hey guys so im trying to use a while loop to add objects to a list. Heres bascially what i want to do: (ill paste actually go after) class x: blah blah choice = raw_input(pick what you want to do) while(choice!=0): if(choice==1): Enter in info for the class: append object to list (A) if(choice==2): print out length of list(A) if(choice==0): break ((((other options)))) as im doing this i can get the object to get added to the list, but i am stuck as to how to add multiple objects to the list in the loop. Here is my actual code i have so far... print "Welcome to the Student Management Program" class Student: def init (self, name, age, gender, favclass): self.name = name self.age = age self.gender = gender self.fac = favclass choice = int(raw_input("Make a Choice: " )) while (choice !=0): if (guess==1): print("STUDENT") namer = raw_input("Enter Name: ") ager = raw_input("Enter Age: ") sexer = raw_input("Enter Sex: ") faver = raw_input("Enter Fav: ") elif(guess==2): print "TESTING LINE" elif(guess==3): print(len(a)) guess=int(raw_input("Make a Choice: ")) s = Student(namer, ager, sexer, faver) a =[]; a.append(s) raw_input("Press enter to exit") any help would be greatly appreciated!

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  • C++ Generic List Assignment

    - by S73417H
    I've clearly been stuck in Java land for too long... Is it possible to do the C++ equivalent of the following Java code: // Method List<Bar> getBars() { return new LinkedList<Bar>(); } // Assignment statement. List<Foo> stuff = getBars(); Where Foo is a sub-class of Bar. So in C++.... std::list<Bar> & getBars() { std::list<Bar> bars; return bars; } std::list<Foo> stuff = getBars(); Hope that makes sense....

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  • Linked List Inserting in sorted format

    - by user2738718
    package practise; public class Node { public int data; public Node next; public Node (int data, Node next) { this.data = data; this.next = next; } public int size (Node list) { int count = 0; while(list != null){ list = list.next; count++; } return count; } public static Node insert(Node head, int value) { Node T; if (head == null || head.data <= value) { T = new Node(value,head); return T; } else { head.next = insert(head.next, value); return head; } } } This work fine for all data values less than the first or the head. anything greater than than doesn't get added to the list.please explain in simple terms thanks.

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  • Flex list-controls - maintain remote data

    - by artemb
    Hello. I have a TileList which represents some remote data. I also have a form which allows me to change the data. And the data may be changed by someone else too. What is the best way to maintain data in the list in an up-to-date state? The simplest option I see is the following: Select an item in the list Edit it in the form Save it. The form submits the data to the server When the server reports success the list re-fetches it's data The very bad thing about this workflow is that the list loses selection (a tree would also loose the nodes' expanded/collapsed state). I would really love to find out another option which would enable the list to maintain it's selection state. Any guesses on how it may be done?

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  • python: creating a list inside a dictionary

    - by user1871081
    I just started using python and I'm trying to create a program that will read a file that looks like this: AAA x 111 AAB x 111 AAA x 112 AAC x 123 ... the file is 50 lines long and I'm trying to make the letters into keys in a dictionary and the numbers lists that correspond with the keys. I want the output to look like this: {AAA: ['111', '112'], AAB: ['111'], AAC: [123], ...} This is what I've tried file = open("filename.txt", "r") readline = file.readline().rstrip() while readline!= "": list = [] list = readline.split(" ") j = list.index("x") k = list[0:j] v = list[p + 1:] d = {} if k in d == False d[k] = [] d[k].append(v) else d[k].append(v) readline = file.readline().rstrip() I keep getting syntax errors on my if statement and I can't figure out what I've done wrong.

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  • improve my code for collapsing a list of data.frames

    - by romunov
    Dear StackOverFlowers (flowers in short), I have a list of data.frames (walk.sample) that I would like to collapse into a single (giant) data.frame. While collapsing, I would like to mark (adding another column) which rows have came from which element of the list. This is what I've got so far. This is the data.frame that needs to be collapsed/stacked. > walk.sample [[1]] walker x y 1073 3 228.8756 -726.9198 1086 3 226.7393 -722.5561 1081 3 219.8005 -728.3990 1089 3 225.2239 -727.7422 1032 3 233.1753 -731.5526 [[2]] walker x y 1008 3 205.9104 -775.7488 1022 3 208.3638 -723.8616 1072 3 233.8807 -718.0974 1064 3 217.0028 -689.7917 1026 3 234.1824 -723.7423 [[3]] [1] 3 [[4]] walker x y 546 2 629.9041 831.0852 524 2 627.8698 873.3774 578 2 572.3312 838.7587 513 2 633.0598 871.7559 538 2 636.3088 836.6325 1079 3 206.3683 -729.6257 1095 3 239.9884 -748.2637 1005 3 197.2960 -780.4704 1045 3 245.1900 -694.3566 1026 3 234.1824 -723.7423 I have written a function to add a column that denote from which element the rows came followed by appending it to an existing data.frame. collapseToDataFrame <- function(x) { # collapse list to a dataframe with a twist walk.df <- data.frame() for (i in 1:length(x)) { n.rows <- nrow(x[[i]]) if (length(x[[i]])>1) { temp.df <- cbind(x[[i]], rep(i, n.rows)) names(temp.df) <- c("walker", "x", "y", "session") walk.df <- rbind(walk.df, temp.df) } else { cat("Empty list", "\n") } } return(walk.df) } > collapseToDataFrame(walk.sample) Empty list Empty list walker x y session 3 1 -604.5055 -123.18759 1 60 1 -562.0078 -61.24912 1 84 1 -594.4661 -57.20730 1 9 1 -604.2893 -110.09168 1 43 1 -632.2491 -54.52548 1 1028 3 240.3905 -724.67284 1 1040 3 232.5545 -681.61225 1 1073 3 228.8756 -726.91980 1 1091 3 209.0373 -740.96173 1 1036 3 248.7123 -694.47380 1 I'm curious whether this can be done more elegantly, with perhaps do.call() or some other more generic function?

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  • latex list environment inside the tabular environment: extra line at top preventing alignment

    - by Usagi
    Hello good people of stackoverflow. I have a LaTeX question that is bugging me. I have been trying to get a list environment to appear correctly inside the tabular environment. So far I have gotten everything to my liking except one thing: the top of the list does not align with other entries in the table, in fact it looks like it adds one line above the list... I would like to have these lists at the top. This is what I have, a custom list environment: \newenvironment{flushemize}{ \begin{list}{$\bullet$} {\setlength{\itemsep}{1pt} \setlength{\parskip}{0pt} \setlength{\parsep}{0pt} \setlength{\partopsep}{0pt} \setlength{\topsep}{0pt} \setlength{\leftmargin}{12pt}}}{\end{list}} Renamed ragged right: \newcommand{\rr}{\raggedright} and here is my table: \begin{table}[H]\caption{Tank comparisons}\label{tab:tanks} \centering \rowcolors{2}{white}{tableShade} \begin{tabular}{p{1in}p{1.5in}p{1.5in}rr} \toprule {\bf Material} & {\bf Pros} & {\bf Cons} & {\bf Size} & {\bf Cost} \\ \midrule \rr Reinforced concrete &\rr \begin{flushemize}\item Strong \item Secure \end{flushemize}&\rr \begin{flushemize}\item Prone to leaks \item Relatively expensive to install \item Heavy \end{flushemize} & 100,000 gal & \$299,400 \\ \rr Steel & \begin{flushemize}\item Strong \item Secure \end{flushemize} & \begin{flushemize}\item Relatively expensive to install \item Heavy \item Require painting to prevent rusting \end{flushemize} & 100,000 gal & \$130,100 \\ \rr Polypropylene & \begin{flushemize}\item Easy to install \item Mobile \item Inexpensive \item Prefabricated \end{flushemize} & \begin{flushemize}\item Relatively insecure \item Max size available 10,000 gal \end{flushemize} & 10,000 gal & \$5,000 \\ \rr Wood & \begin{flushemize}\item Easy to install \item Mobile \item Cheap to install \end{flushemize} & \begin{flushemize}\item Prone to rot \item Must remain full once constructed \end{flushemize} & 100,000 gal & \$86,300\\ \bottomrule \end{tabular} \end{table} Thank you for any advice :)

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  • Subset a data.frame by list and apply function on each part, by rows

    - by aL3xa
    This may seem as a typical plyr problem, but I have something different in mind. Here's the function that I want to optimize (skip the for loop). # dummy data set.seed(1985) lst <- list(a=1:10, b=11:15, c=16:20) m <- matrix(round(runif(200, 1, 7)), 10) m <- as.data.frame(m) dfsub <- function(dt, lst, fun) { # check whether dt is `data.frame` stopifnot (is.data.frame(dt)) # check if vectors in lst are "whole" / integer # vector elements should be column indexes is.wholenumber <- function(x, tol = .Machine$double.eps^0.5) abs(x - round(x)) < tol # fall if any non-integers in list idx <- rapply(lst, is.wholenumber) stopifnot(idx) # check for list length stopifnot(ncol(dt) == length(idx)) # subset the data subs <- list() for (i in 1:length(lst)) { # apply function on each part, by row subs[[i]] <- apply(dt[ , lst[[i]]], 1, fun) } # preserve names names(subs) <- names(lst) # convert to data.frame subs <- as.data.frame(subs) # guess what =) return(subs) } And now a short demonstration... actually, I'm about to explain what I primarily intended to do. I wanted to subset a data.frame by vectors gathered in list object. Since this is a part of code from a function that accompanies data manipulation in psychological research, you can consider m as a results from personality questionnaire (10 subjects, 20 vars). Vectors in list hold column indexes that define questionnaire subscales (e.g. personality traits). Each subscale is defined by several items (columns in data.frame). If we presuppose that the score on each subscale is nothing more than sum (or some other function) of row values (results on that part of questionnaire for each subject), you could run: > dfsub(m, lst, sum) a b c 1 46 20 24 2 41 24 21 3 41 13 12 4 37 14 18 5 57 18 25 6 27 18 18 7 28 17 20 8 31 18 23 9 38 14 15 10 41 14 22 I took a glance at this function and I must admit that this little loop isn't spoiling the code at all... BUT, if there's an easier/efficient way of doing this, please, let me know!

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  • Linked list recursive reverse

    - by Phoenix
    I was looking at the code below from stanford library: void recursiveReverse(struct node** head_ref) { struct node* first; struct node* rest; /* empty list */ if (*head_ref == NULL) return; /* suppose first = {1, 2, 3}, rest = {2, 3} */ first = *head_ref; rest = first->next; /* List has only one node */ if (rest == NULL) return; /* put the first element on the end of the list */ recursiveReverse(&rest); first->next->next = first; /* tricky step -- see the diagram */ first->next = NULL; /* fix the head pointer */ *head_ref = rest; } What I don't understand is in the last recursive step for e.g if list is 1-2-3-4 Now for the last recursive step first will be 1 and rest will be 2. So if you set *head_ref = rest .. that makes the head of the list 2 ?? Can someone please explain how after reversing the head of the list becomes 4 ??

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  • std::list iterator: get next element

    - by sheepsimulator
    I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems != dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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  • std::list : get next element

    - by sheepsimulator
    I'm trying to build a string using data elements stored in a std::list, where I want commas placed only between the elements (ie, if elements are {A,B,C,D} in list, result string should be "A,B,C,D". This code does not work: typedef std::list< shared_ptr<EventDataItem> > DataItemList; // ... std::string Compose(DataItemList& dilList) { std::stringstream ssDataSegment; for(iterItems = dilList.begin(); iterItems = dilList.end(); iterItems++) { // Lookahead in list to see if next element is end if((iterItems + 1) == dilList.end()) { ssDataSegment << (*iterItems)->ToString(); } else { ssDataSegment << (*iterItems)->ToString() << ","; } } return ssDataSegment.str(); } How do I get at "the-next-item" in a std::list using an iterator? I would expect that it's a linked-list, why can't I get at the next item?

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  • C# Changing Objects within a List

    - by kwong22
    Hi, I'm having a little problem changing members of an object in a list using a found index. So this is the method I am currently working with: static void addToInventory(ref List<baseItem> myArray, baseItem item, float maxAmount, ref float currentAmount) { if (currentAmount + item.getWeight() <= maxAmount) { Console.WriteLine("item.Quantity = {0}", item.Quantity); if (myArray.Contains(item)) { Console.WriteLine("Item ({0}) already exists", item.Name); int id = myArray.IndexOf(item); myArray[id].Quantity += item.Quantity;//Change occurs in this line, item.Quantity becomes the same as myArray[id].Quantity } else { Console.WriteLine("Adding new item ({0})", item.Name); myArray.Add(item); } currentAmount += item.getWeight(); } else { Console.WriteLine("Inventory full"); } myArray.Sort(); } This method takes several parameters including the inventory/list. I check if the item fits in and if it does, I see if there is another item of the same name in the list, find the index, and add more of the item. However, the quantity of the item added suddenly becomes the same as the quantity of the item in the list. For some reason, this also changes the quantity of the item outside of the list. So therefore, instead of quantities adding up like this: 1, 2, 3, 4, they add up like this: 1, 2, 4, 8. I've just started to learn how to use lists so if there is anything I'm missing, don't hesitate to criticize. Thanks in advance.

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  • List modification in Python

    - by user2945143
    We are given an algorithm to modify a list of numbers from 1 to 28. There are 5 steps in the algorithm. We have written functions for each step (all correct). We need to write a function that combines all 5 steps. The algorithm modifies the list to get a value. Each time you get a new value, you use the list created by the algorithm from the previous step. This is what we have gotten so far for the code: get_card_at_top_index(insert_top_to_bottom(triple_cut((move_joker_2( move_joker_1(deck)))))) When we run the code to generate the get_card_at_top_index, the first answer is correct. However, the rest are not. Instead of using from the new list, python uses the value that it generated from the last step. What did we do wrong? UPDATE: The other 5 codes passed the tests, they are correct. Code 1 (List) = list1 Code 2 (list1) = list2 Code 3 (list2) = list3 Code 4 (list3) = list4 Code 5 (list4) = list5 we generate a number from 5. We need to run the algorithm again to generate 25 more numbers. We will use list 5 start from step 1

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  • F# insert/remove item from list

    - by Timothy
    How should I go about removing a given element from a list? As an example, say I have list ['A'; 'B'; 'C'; 'D'; 'E'] and want to remove the element at index 2 to produce the list ['A'; 'B'; 'D'; 'E']? I've already written the following code which accomplishes the task, but it seems rather inefficient to traverse the start of the list when I already know the index. let remove lst i = let rec remove lst lst' = match lst with | [] -> lst' | h::t -> if List.length lst = i then lst' @ t else remove t (lst' @ [h]) remove lst [] let myList = ['A'; 'B'; 'C'; 'D'; 'E'] let newList = remove myList 2 Alternatively, how should I insert an element at a given position? My code is similar to the above approach and most likely inefficient as well. let insert lst i x = let rec insert lst lst' = match lst with | [] -> lst' | h::t -> if List.length lst = i then lst' @ [x] @ lst else insert t (lst' @ [h]) insert lst [] let myList = ['A'; 'B'; 'D'; 'E'] let newList = insert myList 2 'C'

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  • Convert List of one type to Array of another type using Dozer

    - by aheu
    I'm wondering how to convert a List of one type to an array of another type in Java using Dozer. The two types have all the same property names/types. For example, consider these two classes. public class A{ private String test = null; public String getTest(){ return this.test } public void setTest(String test){ this.test = test; } } public class B{ private String test = null; public String getTest(){ return this.test } public void setTest(String test){ this.test = test; } } I've tried this with no luck. List<A> listOfA = getListofAObjects(); Mapper mapper = DozerBeanMapperSingletonWrapper.getInstance(); B[] bs = mapper.map(listOfA, B[].class); I've also tried using the CollectionUtils class. CollectionUtils.convertListToArray(listOfA, B.class) Neither are working for me, can anyone tell me what I am doing wrong? The mapper.map function works fine if I create two wrapper classes, one containing a List and the other a b[]. See below: public class C{ private List<A> items = null; public List<A> getItems(){ return this.items; } public void setItems(List<A> items){ this.items = items; } } public class D{ private B[] items = null; public B[] getItems(){ return this.items; } public void setItems(B[] items){ this.items = items; } } This works oddly enough... List<A> listOfA = getListofAObjects(); C c = new C(); c.setItems(listOfA); Mapper mapper = DozerBeanMapperSingletonWrapper.getInstance(); D d = mapper.map(listOfA, D.class); B[] bs = d.getItems(); How do I do what I want to do without using the wrapper classes (C & D)? There has got to be an easier way... Thanks!

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  • No Matching Function Error for inserting into a list in c++

    - by Josh Curren
    I am getting an error when I try to insert an item into a list (in C++). The error is that there is no matching function for call to the insert(). I also tried push_front() but got the same error. Here is the error message: main.cpp:38: error: no matching function for call to ‘std::list<Salesperson, std::allocator<Salesperson> >::insert(Salesperson&)’ /usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/bits/list.tcc:99: note: candidates are: std::_List_iterator<_Tp> std::list<_Tp, _Alloc>::insert(std::_List_iterator<_Tp>, const _Tp&) [with _Tp = Salesperson, _Alloc = std::allocator<Salesperson>] /usr/lib/gcc/i686-pc-cygwin/4.3.4/include/c++/bits/stl_list.h:961: note: void std::list<_Tp, _Alloc>::insert(std::_List_iterator<_Tp>, size_t, const _Tp&) [with _Tp = Salesperson, _Alloc = std::allocator<Salesperson>] Here is the code: #include <stdlib.h> #include <iostream> #include <fstream> #include <string> #include <list> #include "Salesperson.h" #include "Salesperson.cpp" #include "OrderedList.h" #include "OrderedList.cpp" using namespace std; int main(int argc, char** argv) { cout << "\n------------ Asn 8 - Sales Report ------------" << endl; list<Salesperson> s; int id; string fName, lName; int numOfSales; string year; std::ifstream input("Sales.txt"); while( !std::getline(input, year, ',').eof() ) { input >> id; input >> lName; input >> fName; input >> numOfSales; Salesperson sp = Salesperson( id, fName, lName ); s.insert( sp ); //THIS IS LINE 38 ************************** for( int i = 0; i < numOfSales; i++ ) { double sale; input >> sale; sp.sales.insert( sale ); } } cout << endl; return (EXIT_SUCCESS); }

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  • Hibernate Query for a List of Objects that matches a List of Objects' ids

    - by sal
    Given a classes Foo, Bar which have hibernate mappings to tables Foo, A, B and C public class Foo { Integer aid; Integer bid; Integer cid; ...; } public class Bar { A a; B b; C c; ...; } I build a List fooList of an arbitrary size and I would like to use hibernate to fetch List where the resulting list will look something like this: Bar[1] = [X1,Y2,ZA,...] Bar[2] = [X1,Y2,ZB,...] Bar[3] = [X1,Y2,ZC,...] Bar[4] = [X1,Y3,ZD,...] Bar[5] = [X2,Y4,ZE,...] Bar[6] = [X2,Y4,ZF,...] Bar[7] = [X2,Y5,ZG,...] Bar[8] = ... Where each Xi, Yi and Zi represents a unique object. I know I can iterate fooList and fetch each List and call barList.addAll(...) to build the result list with something like this: List<bar> barList.addAll(s.createQuery("from Bar bar where bar.aid = :aid and ... ") .setEntity("aid", foo.getAid()) .setEntity("bid", foo.getBid()) .setEntity("cid", foo.getCid()) .list(); ); Is there any easier way, ideally one that makes better use of hibernate and make a minimal number of database calls? Am I missing something? Is hibernate not the right tool for this?

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  • how to bind a list to a dropdown list in gridview

    - by user3721173
    I have a GridView that it contain a Drop-down list.I have a list that wanna to bind this list to drop-down in gridview. <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False"OnSelectedIndexChanged="GridView1_SelectedIndexChanged" OnRowDataBound="GridView1_RowDataBound"> <Columns> <ItemTemplate> <asp:Label ID="Label2" runat="server"></asp:Label> <asp:DropDownList ID="DropDownList3" runat="server" AppendDataBoundItems="True" OnSelectedIndexChanged="DropDownList3_SelectedIndexChanged1" > </asp:DropDownList> </ItemTemplate> </asp:TemplateField> </Columns> and protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e) { DropDownList dropdown = (DropDownList)e.Row.FindControl("DropDownList3"); ClassDal obj = new ClassDal(); List<phone> list = obj.GetAll(); dropdown.DataTextField = "phone"; dropdown.DataValueField = "id"; dropdown.DataSource = list.ToList(); dropdown.DataBind(); } and namespace sample_table { public class ClassDal { public List<phone> GetAll() { using (PracticeDBEntities1 context = new PracticeDBEntities1()) { return context.phone.ToList(); } } } } but i received this exception :Object reference not set to an instance of an object on the row: dropdown.DataTextField = "phone";

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